1. Field of the Invention
The present invention relates to an electronic parking brake apparatus, and more particularly, to an electronic parking brake apparatus, in which a sensor for measuring tension of a parking cable is implemented with a load cell based on a strain gauge, and is mounted on a cable ferrule, thereby reducing the length of the electronic parking brake apparatus.
2. Description of Related Art
In general, parking brakes for vehicles are used for stopping the vehicle or preventing movement of the vehicle during parking by a driver stepping on a parking brake pedal or pulling a parking brake lever. Recently an electronic parking brake (EPB) is used, which is operated by simple manipulation of a switch.
This EPB is configured so that, when a switch is pushed to drive a motor, a parking cable is pulled by rotation of the motor, and thereby generating a uniform braking force for each rear wheel. This EPB need measurement of the magnitude of tension of the parking cable pulled by the motor. To this end, the EPB measures force that is typically generated through variation in displacement of a spring, and precisely controls a locked state of the parking cable and a driving force of the motor on the basis of the measured force.
An EPB unit using a spring displacement sensor will be described below with reference to the accompanying drawings.
FIG. 1 illustrates the configuration of a conventional EPB unit on which a spring displacement sensor is mounted.
The EPB unit 100 includes an electronic control unit (ECU) 110 controlling a locking or unlocking force of a parking brake through power supplied by manipulation of a switch, a driving means 120 tightening or loosening the parking cable 140 manipulating a brake mechanism for rear wheels by means of driving of the EPB ECU 110, and a sensing unit 160 measuring tension of the parking cable 140 tightened or loosened by the driving means 120 and then sending the measured signal to the EPB ECU 110.
The EPB unit 100 also includes a motor 121 installed in a case 130 having a predetermined shape so as to run backwards or forwards according to the manipulation of the switch, a driving gear 122 rotatably engaged with a rotating shaft of the motor 121, and a movable nut 124 engaged with a screw 123 and generating a linear moving force so as to pull or loosen the parking cable 140 by means of rotation of the driving gear 122.
Here, the sensing unit 160 is configured so that an equalizer connecting shaft 162 thereof connected with the parking cable 140 cooperates with the movable nut 124, thereby causing a movable pressure member 163 therein to compress a spring 161.
At this time, a displacement sensor 164 such as a hall sensor located in the sensing unit 160 detects displacement of the movable pressure member 163 or the spring 161, and sends the detected value to a sensor ECU 170. Then, the sensor ECU 170 calculates a level of load, and then sends the calculated result to the EPB ECU 110. In this process, the tension of the parking cable 140 is measured when the parking cable 140 is pulled.
In this manner, length of the case 130 is increased in a longitudinal direction of the parking cable 140 due to additional length of the sensing unit 160 located therein, which has an adverse influence on a layout of the vehicle.
Further, the sensor ECU 170 sending the measured value to the EPB ECU 110 is attached on one side of the sensing unit 160, and thus moves together when the sensing unit 160 moves. Further, an interface 180 connected between the sensor ECU 170 and the EPB ECU 110 moves together when the sensing unit 160 moves. In this process, the interface 180 interferes with the interior of the case 130 to be shorted out or cut off.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.